This invention relates to a seal for retaining lubricant around a journal bearing in a rock bit or drill bit for drilling oil wells or the like. More particularly, this invention relates to seal rings having a dynamic seal surface profile that is constructed with at least two contact pressure maximas that form multiple barriers to control the passage of grease and/or drilling fluid thereacross, thereby providing optimal properties of sealability and wear resistance to maximize seal service life.
Rock bits are employed for drilling wells, blast holes, or the like in subterranean formations for oil, gas, geothermal steam, minerals, and the like. Such drill bits have a body connected to a drill string and a plurality, typically three, of hollow cutter cones mounted on the body for drilling rock formations. The cutter cones are mounted on steel journals or pins integral with the bit body at its lower end. In use, the drill string and/or the bit body are rotated in the bore hole, and each cone is caused to rotate on its respective journal as the cone contacts the bottom of the bore hole being drilled. High temperatures and pressures are often encountered when such rock bits are used for drilling in deep wells.
When a drill bit wears out or fails as a bore hole is being drilled, it is necessary to withdraw the drill string for replacing the bit. The amount of time required to make a round trip for replacing a bit is essentially lost from drilling operations. This time can become a significant portion of the total time for completing a well, particularly as the well depths become great. It is therefore quite desirable to maximize the service life of a drill bit in a rock formation. Prolonging the time of drilling minimizes the time lost in xe2x80x9cround trippingxe2x80x9d the drill string for replacing the bits. Replacement of a drill bit can be required for a number of reasons, including wearing out or breakage of the structure contacting the rock formation.
One reason for replacing the rock bits include failure or severe wear of the journal bearings on which the cutter cones are mounted. These bearings can be friction- or roller-type bearings, and can be subject to high loads, high hydrostatic pressures in the hole being drilled, high temperatures due to drilling, elevated temperatures in the formation being drilled, as well as harmful abrasive particles originating from the formation being drilled. The journal bearings are lubricated with grease adapted to such severe conditions. Such lubricants are a critical element in the life of a rock bit. A successful grease should have a useful life longer than other elements of the bit so that premature failures of bearings do not unduly limit drilling.
The grease is retained within the rock bit to lubricate the journal bearings by a journal bearing seal, typically an O-ring type of seal. The seal must endure a range of temperature and pressure conditions during the operation of the rock bit to prevent the grease from escaping and/or contaminants from entering the bearing and, thereby ensure that the journal bearings are sufficiently lubricated. Elastomer seals known in the art are conventionally formed from a single type of rubber or elastomeric material, and are generally formed having identically configured dynamic and static seal surfaces, i.e., having symmetrically configured sealing surfaces. The rubber or elastomeric material selected to form such a seal has particular hardness, modulus of elasticity, wear resistance, temperature stability, and coefficient of friction. Additionally, the particular geometric configuration of the seal surfaces produces a given amount of seal deflection that defines the degree of contact pressure or xe2x80x9csqueezexe2x80x9d applied by the dynamic and static seal surfaces against respective journal bearing and cone surfaces.
The wear, temperature, and contact pressure conditions that are encountered at the dynamic seal surface are different than those encountered at the static seal surface. Therefore, the type of seal material and seal geometry that is ultimately selected to form both seal surfaces represents a compromise between satisfying the operating conditions that occur at the different dynamic and static seal surfaces. Because of the different operating conditions at each seal surface, conventional seals formed from a single-type of material, having symmetrically configured sealing surface, often display poor wear resistance and poor temperature stability at the dynamic seal surface where wear and temperature conditions, under high-temperature operating conditions, are the most aggressive. Accordingly, the service life of rock bits that contain such seals are defined by the limited capability of the seal itself.
U.S. Pat. No. 5,842,701 discloses a seal ring used within a rotary cone rock bit that has a static seal surface that is smaller in radius than a dynamic seal surface, i.e., a seal ring that is asymmetric. The seal ring dynamic seal surface is designed having a continuous surface, i.e., one that is in continuous contact with an adjacent rock bit dynamic surface when moving axially therealong. The seal ring is designed in this manner to provide contact forces against adjacent static and dynamic rock bit surfaces that are best suited for the different operating conditions at each such surface. Additionally, the seal ring can include a dynamic seal surface that formed from a material that is different than that of the static seal surface to further enable the seal ring to meet the specific operating conditions at each static and dynamic surface.
U.S. Pat. No. 5,842,700 discloses a seal ring used within a rotary cone rock bit that includes a dynamic seal surface that is formed from a material different than the static seal surface. The dynamic seal surface is formed from a composite material that provides improved wear resistance when compared to a non-composite elastomer. The dynamic seal surface is formed from a nonelastomeric polymeric fabric material that is specially designed to enhance the wear life of the seal when positioned adjacent the rock bit dynamic surface.
When designing seals for use in such applications it is desirable to optimize not only the property of wear resistance but sealability, i.e., the ability of the seal to retain lubricant with the rock bit journal and prevent drilling fluid from entering the rock bit journal. Typically, improvements in seal ring wear life provide compromised sealability and visa versa. While the above-described seal rings do provide an improved degree of wear resistance when compared to other seal rings, improvements in sealability are still desired.
It is, therefore, desired that journal bearing seals be designed to optimize properties of both wear resistance and sealability. It is additionally desired that such journal bearing seals be designed to enable their use without the need to unduly modify the application device, e.g., existing seal cavity, to permit their retrofit use in a number of existing applications.
There is, therefore, provided in practice of this invention a seal ring having a dynamic seal surface comprising multiple surface elements that are configured to provide multiple barriers to the migration of grease and/or drilling fluid thereacross. A related characteristic of seal rings of this invention is that the dynamic seal surface comprise more than one contact pressure profile maxima when installed within a rock bit against a rock bit rotary dynamic surface.
Seal rings of this invention comprises an annular elastomeric ring-shaped body comprising a dynamic seal surface, disposed along a first body portion, having at least two outwardly projecting surface elements, and a static seal surface disposed along a second body portion. The seal dynamic seal surface can be disposed along the seal outside diameter or inside diameter, in the case where the seal ring is a radial sealing element, or the seal dynamic seal surface can be disposed along either seal axial surface, in the case where the seal ring is an axial sealing element. The dynamic seal surface elements are separated by a recessed portion, or discontinuity, that extends around the seal dynamic surface and that may or may not be visible once the seal is installed within the rock bit.
At least a portion of the dynamic seal surface, e.g., at least a portion of one of the surface elements, can be formed from a material different from that used to form the seal body. In an example embodiment, a wear surface of one of the surface elements is formed from a material that is more wear resistant than that used to form the remaining seal dynamic surface and/or the remaining seal body. In a preferred embodiment, the wear surface is formed from a composite material comprising a fabric of nonelastomeric polymeric material that is bonded together with an elastomeric material.
Additional embodiments of seals of this invention include those where: (1) the seal is formed entirely from a single-type of elastomeric material; (2) the seal comprises a seal body formed from a material different than that of the dynamic seal surfaces; and (3) the seal comprises a seal body formed from a material different than that both of the dynamic seal surfaces and the static seal surface.
A seal construction comprising projecting dynamic seal surface elements is advantageous when compared to conventional seals having a single dynamic seal surface element because each independent projecting element can be tailored both in size/shape and in the material of construction to provide particular dynamic sealing characteristics at each respective rock bit rotary dynamic surface. For example, the surface elements can be configured to each provide a particular barrier function, by producing a particular contact pressure against a respective surface of the rock bit, to complement the different operating conditions along the rock bit dynamic surface, thereby optimizing sealability. Additionally, the surface elements can be formed from the same or different materials that are selected to better accommodate the different temperature and wear conditions that exist at each edge portion of the rock bit dynamic surface during the drilling operation, thereby optimizing wear resistance.
Further, seal constructions comprising multiple dynamic surface elements include a recessed portion that can be designed to retain grease therein, when the seal is installed within the rock bit, to further reduce friction-related wear, which feature is not provided by conventional seal constructions comprising only a single surface element. The recessed dynamic surface portion can also be designed to act as a buffer zone to prevent the unwanted passage of fluids between dynamic surface elements and into or out of the rock bit. Thus, the seal dynamic surface elements and recessed portion act together to provide improved resistance to migration of fluid thereacross, thereby providing improved sealability.
For these reasons, seals constructed according to this invention are well adapted to accommodate the different operating conditions and sealing requirements that exist both at the dynamic and static surfaces of the seal to ensure optimal seal performance and, thereby enhance the service life of rock bits that contain such seals.